The invention herein relates to fibrous thermal insulations. More particularly, it relates to such insulations which can be manufactured in flat or board form and then bent or curved to form insulation jackets around pipes, vessels and similar curved structures.
Fibrous thermal insulations, particularly those using glass fibers and mineral wool fibers, have been commonly used for pipe insulation and the like for a number of years. Such insulation in a variety of configurations is generally represented by FIGS. 1A through 1C. FIG. 1A shows fibrous insulation wherein the orientation of the fibers is circumferential. Where the fiber density is low (less than 1.5 pounds per cubic foot ("pcf")), fibrous batts having horizontal fiber orientation can be curved to conform to the circumferential pattern shown in FIG. 1A. There is, however, a decided tendency of such materials to resile to their original flat configuration, and they must be securely held closed around the pipes to prevent their opening out and pulling away from the pipes. At higher densities, (1.5 pcf or higher) the batts or boards of fiber are generally too rigid to be curved after formation, particularly to conform to the outer surface of small diameter pipe. In such cases the fibers when unbonded are molded to the circumferential shape and then bonded in that shape by being coated with a resin binder which is subsequently cured to form a rigid curved structure. Alternatively, fibers with uncurved binder can be bent to the desired curvature and then bonded by curing the binder. Typical of such molded fiber glass materials are those sold under the trademark FLAME-SAFE by Johns-Manville Corporation and which have fiber densities on the order of 3.5 to 4 pcf.
It has also been known to build up thick sections of circumferentially oriented fibrous insulations by forming spirals of very thin layers as shown in FIG. 1C, or by using concentric circumferential shells as shown in U.S. Pat. No. 3,886,024.
Thus, with higher density materials it has always been necessary to take elaborate steps to form curved pipe insulation. In addition, the molded insulations must be molded to individual pipe sizes and are thus not individually adaptable to different pipe sizes, but rather a large inventory of various premolded sizes must be maintained by the user.
In an alternative approach to forming curved fibrous pipe insulation, fibers have been oriented radially as shown in U.S. Pat. Nos. 2,949,953 and 3,012,923. Single layers have been used, or windings of multiple layers. A typical configuration is shown in FIG. 1B. Such a configuration allows for a great deal of flexibility and permits the insulation to be bent around relatively small diameter pipes. However, the radial fiber orientation has low thermal resistance. Thus, the radial material, while gaining significant flexibility over the circumferential material, provides significantly less thermal insulation.